This invention relates to pulverizers and more particularly to a novel and improved blade sweep for use in vertical spindle pulverizers.
In conventional vertical spindle pulverizers, a material to be pulverized, such as raw coal is distributed onto a rotating grinding bowl to be ground into fine, powder-like particles by a number of stationary rollers. These pulverizers are commonly known as roll-and-race or ball-and-track pulverizers. Pulverizers pare materials down to a fine particle size via crushing pressure, impact and attrition. After fluidization, the particles are suspended and then transported through an outlet and then through discharge pipes to be combusted (e.g. in a power plant boiler) by air that has been forced upwardly around the circumference of the bowl.
Because of the nature of mining, many ungrindable objects (e.g. rocks, shale, iron pyrites, tramp iron, etc.) and herein referred to as reject material, are included in the material to be ground. These objects, which are too heavy to be pneumatically transported through the pulverizer outlet, are rejected by the system and pushed over the edge of the bowl and land underneath in an under-bowl area above the floor. To inhibit excessive accumulation, potential fires and/or explosions, this rejected material must be constantly discharged from the under-bowl area. Presently known sweeps used for removal of such reject material are connected to and rotate with the bowl hub or skirt near the floor. This apparatus, commonly referred to as a plow or scraper, is generally very heavy, difficult to maintain and expensive. In most cases, a vertical pivot wears allowing the assembly to make contact with the floor, or a coaxial spring arrangement fails, causing floor damage and the potential for igniting under-bowl fires.
A brush sweep described in U.S. Pat. No. 5,480,099, assigned to the assignee of the present application, utilizes a plurality of cables. This provides a sweep that is significantly lighter, easier to maintain and relatively inexpensive as compared to previously known sweeps. The plow, scraper, and brush sweep rotate in a horizontal plane to clear the reject material from the floor and push the reject material down an outlet in the floor to be collected in a hopper and be discarded.
Prairie et al. U.S. Pat. No. 5,904,307 discloses a scraper for a pulverizer, including a bracket attached to a rotating spindle hub, a shaft supported at one end only and extending radially out from the bracket and rotating about the vertical axis with the spindle. A scraper element is pivotally mounted to rotate about the axis of the shaft and a torsion spring is used to bias the shaft to a scraping position.
A blade sweep for a pulverizer is disclosed. In the first embodiment disclosed the blade sweep is secured to the spindle skirt. This blade sweep includes a mounting base mounted to rotate with the spindle skirt about a vertical axis, an axle extending parallel to and supported for rotation about the longitudinal axis of the spindle at more than one point along the axle by the mounting base. A plurality of pivot brackets are disposed at axially spaced positions along the axle and are rigidly affixed to the axle, preferably by welding, to rotate with the axle, a sweep blade extends along and is located below the axle and the mounting bar and is affixed to the axle to rotate with the axle. A bias assembly resists upward blade movement with the axle and returns the blade to a vertical sweeping position. The blade is easily adjusted vertically end to end and may be easily replaced as required. In the second embodiment the blade sweep is secured to the underside of the bowl.